On examination, I found that many of the RSRD prestige classes could be easily excluded from consideration. In many cases they could be adequately modeled using other talents, bringing little more than the option of using abilities from more than one class. In other cases they may be better modeled as specific abilities gained through other classes, such as the Archmage’s ‘High Arcana’ abilities being attached to magic-related talents at an appropriate tier.

Arcane Trickster

Archmage

Blackguard

Dragon Disciple

Duelist

Eldritch Knight

Hierophant

Horizon Walker

Loremaster

Mystic Theurge

Thaumaturgist

Many RSRD prestige classes do suggest archetypes that could be rewarded with capstone talents, but their implementation in the RSRD makes them unneeded. I like the idea of an Archmage archetype, it sounds like the sort of thing that could reasonably be a capstone, and the expected high-level requirements might even include the abilities I would use to model the benefits now seen, but it needs to offer something that isn’t otherwise available.

However, I do have lots of source books to work from, I’m pretty sure I can come up with some good capstones without a lot of work, apart from packing them around.